How to tell when your iPhone audio is being rerouted to an external device?

Question

I would like to be notified when my iPhone's audio is being re-routed to another device , say if I connect it to an external Hi-fi system (an MFi device). Put another way, how do I detect if the audio is playing from my iPhone vs. another device when it happens?

How should I go about doing this?

Answer 1

Read Apple's Audio Session documentation on how to request and handle Audio Session route change notifications, and what kind of audio notifications are possible.